Aircraft are launched from aircraft carriers using jet blast deflectors (JBDs). They are used to deflect the jet blast upwards and over the flight deck, thereby protecting the ship's superstructure, other planes/equipment and the personnel conducting launch operations (there are many accounts of sailors lost overboard when struck by the blast of modern jets). The engine plume of a modern aircraft engine at full military power deposits an intense thermal flux onto the JBD, which utilizes nonskid coated and water-cooled aluminum panels to deflect the jet plume upward. Cooling is actively achieved using seawater.
When stowed, the JBD is flush with the carrier deck. The JBD panel to which the elevating gear is attached occupies a pit region cut out of the deck. All JBD's in use today are 14′ along the vertical edge. When raised to the 50° angle used for a take-off they are 11′ in height above the deck. They are made up from 6′ wide panels. The Legacy Mk7 Mod 1 JBD is constructed from 4 of these panels (it is therefore 24′ wide). The Legacy Mk 7 Mod 2 system has 6 panels. It is therefore 36′ in width. Both types are found on all aircraft carriers in service today. JBD panels are raised in pairs by a hydraulic system and linkage assembly. This system is housed in a space beneath the stowed JBD.
The JBD is subjected to a thermal cycle during each launch. First, the JBD is positioned flush with the deck surface so that an aircraft can roll over it and assume its launch position. The JBD is then raised for take-off to provide flight deck protection. Initially, only a fraction of the engine's full military power is applied. However, once a launch decision is made, the JBD is subject to full military power for a specific period of time. In a delayed take-off, the engines are at full power for a significantly longer period. After launch the JBD is quickly rotated flush with the deck to allow the next aircraft to roll over the structure as it is positioned for take-off.
Before a new plane can roll into the launch position, the JBD surface must cool below the temperature that can cause damage to the aircraft tires. The time taken for this determines how quickly the next aircraft can be rolled into position. Since it is desirable to launch the carrier's air wing as quickly as possible, this cooling time needs to be minimized.
Fully armed carrier based aircraft are very heavy. When such an aircraft rolls over the JBD during positioning for take-off, this load is applied to the JBD through the tires. One of the JBD's is located in the aircraft recovery part of the flight deck. If a single wheel strikes the structure during landing, the JBD can experience loads that are much higher than during rollover.
The panels are also subjected to other loads—particularly impacts from accidental tail hook drops and from foreign objects emitted from the engines. These structures must therefore support significant static and dynamic loads. Since the rate at which the JBD surface can be cooled determines how long the next plane must wait before it can cross the JBD, the rate of heat dissipation for these structures is a critical performance metric. JBD's are therefore structures which must support significant compressive and bending stresses while also being capable of rapidly dissipating high heat fluxes.
The current use of a seawater-cooled system results in significant weight and maintenance penalties. The plumbing and water pumping systems contribute a significant amount of weight for each JBD; a Nimitz class aircraft carrier with four catapult launchers therefore has a tremendous amount of topside weight committed to JBD's. Reducing weight is highly desirable, and there is considerable interest in using JBD cooling water for other purposes.
Together with the possibility of a potentially large weight reduction there is therefore a need in alternative approaches for jet blast deflection. Moreover, there is a need in jet blast deflection that can be easily maintained and not disrupt existing launch and aircraft recovery operations.
A limitation in the art is that non passive JBD design still requires blasts of cooling fluid or air to remove the heat input by an aircraft launch.
There is therefore a need for a JBD system and method that may operate in a passive manner.